The strikes began on Saturday afternoon and continued into the early hours on Sunday in what the Israeli army described as a "prolonged" operation against the Hamas group which fired nearly 40 Qassam rockets at Israeli towns.
The rocket barrage, which lightly wounded six Israelis, was the Islamic group's first major attack since the Gaza pullout. Hamas said it fired rockets in retaliation to the explosion at a Gaza rally on Friday it blamed on Israel which killed 15, including its fighters, and injured scores of others.
Israel mounted air strikes on Gaza at least 12 times since Saturday afternoon. While two Hamas fighters were killed in the Israeli strike on Saturday afternoon, 15 people were injured when Israeli warplanes struck a school in crowded Gaza city early on Sunday.
The blast struck the al-Arkam school, which was established by the late founder of the Hamas group, Shaikh Ahmad Yassin.
Ambulances raced to the scene after the explosion in the Tufah neighbourhood, a densely populated area and Hamas stronghold.
The blast collapsed part of the school, and caused damage to at least five nearby homes. Hospital officials said women and children were among the wounded, and one person was in serious condition.
Electricity in the neighbourhood was knocked out, and dozens of people ran in the streets after the attack.
Soon after, in another strike, Israeli helicopters fired three missiles in the northern Gaza Strip.
Israeli warplanes struck Gaza
City's al-Arkam school
The Israeli army said it attacked a weapons-storage facility in the Jabaliya refugee camp used by the Popular Resistance Committees and struck a building in Bait Hanun housing the offices of the Popular Front for the Liberation of Palestine.
Residents in Bait Hanun said the PFLP building suffered heavy damage, but said no one was believed to be inside at the time.
A similar airstrike struck the Jabaliya refugee camp early on Sunday, residents said. The missile fell in an open area and caused no casualties, they said.
A short while earlier, Israeli planes attacked two buildings in the southern city of Khan Yunus which were used by the resistance group, Al Aqsa Martyrs' Brigades.
On Saturday afternoon, Israeli aircraft fired five missiles at two cars in the al-Zaitun neighbourhood of Gaza City, but there were conflicting reports on the number of casualties.
The Palestinian Interior Ministry said two were killed, while medical officials and radio reports said four were killed. Nine people were wounded in this attack.
The Israeli army said the air strike hit two vehicles, one carrying weapons and the other carrying Hamas men.
Relatives identified the two dead men as Hamas fighters.
At least 15 were hurt in the
Israeli strike on al-Arkam school
A senior Israeli commander early on Sunday said a "prolonged" operation against the Hamas group had begun, and hinted that Hamas leaders could be targeted.
Major Geneneral Yisrael Ziv, the army's head of operations, spoke to The Associated Press after Israel launched a pair of air strikes in the Gaza Strip, including one missile attack that hit a school in a crowded neighbourhood in Gaza City.
"It was decided to launch a prolonged and constant attack on the Hamas," Ziv said. He said the attacks would target "all faces" of Hamas.
Asked whether the lives of Hamas' leaders were in danger, he said: "Let them decide for themselves."
Israel killed dozens of Hamas fighters during four years of fighting, but had halted the practice since a February ceasefire declaration.
Earlier, Palestinian Information Minister Nabil Shaath denounced the strikes as an "act of criminal aggression". He also accused Israel of trying to destroy a temporary ceasefire that has largely held since February.
Hamas vowed to avenge the attack, calling on its members to strike Israel "in every spot of our occupied land".
While respecting the ceasefire agreed to in February, the group maintains it has the right to respond to alleged violations by Israel.
Egypt called on both parties to stop the escalation. Foreign
Minister Ahmed Aboul Gheit urged Palestinian factions to keep
the truce. Criticising Israel, he described the bombing of the
strip as a violation of international law.
An Israeli army tank moves into
the Gaza Strip on Saturday
On Saturday evening, Sharon convened his Security Cabinet,a group of senior ministers, to approve a series of military operations culminating with a ground incursion into Gaza.
Israeli security officials said that "Operation First Rain" would include artillery fire, air strikes and other targeted attacks.
The operation will grow in intensity, leading up to a ground operation unless the Palestinian security takes action to halt the rocket attacks or Hamas ends the attacks itself.
The ground operation would require final approval from the
full Cabinet, the officials added.
Israel's closure of all Palestinian areas, imposed on Saturday, would continue.
The small number of labourers allowed to work in Israel also would not be allowed through Gaza border crossings and West Bank checkpoints.
Israel also set up five artillery cannons on the Gaza Strip border, near the Israeli communal farm of Nahal Oz.
Seven armoured personnel carriers guarded the cannons, and soldiers appeared to be settling in, setting up a command post and rolling out barbed wire.
At another border staging area, near the Israeli communal farm of Miflassim, four armoured personnel carriers, five tanks and four huge D-9 bulldozers joined about 30 armoured vehicles that are regularly deployed there.
In Gaza City, several loud sonic booms were heard throughout the day as Israeli warplanes flew overhead, emitting white smoke.
Frantic residents ran for cover, but no casualties were reported. Palestinians accused Israel of launching "fake" air strikes to terrify the population.
Mourners carry Hamas members'
bodies at their funeral in Jabaliya
Earlier on Saturday, about 10,000 mourners attended prayers for 10 of the dead killed in an explosion at Friday's Hamas rally. At least 15 Palestinians were killed and scores wounded.
After the ceremony at a Jabalia mosque, the crowd split into three processions, with Hamas holding a separate march for four of its dead.
Men fired guns in the air, and women watching from balconies threw rice into the crowd.
Hamas blamed Israel for Friday's blast and said it fired rockets on Israeli border towns in retaliation. However, the Palestinian Authority held the resistance group responsible, saying its members apparently mishandled explosives, and renewed demands that armed groups stop flaunting their weapons in public.
The exact casualty toll from the Hamas rally remained unclear on Saturday.
Doctors at two Gaza hospitals said they had 15 bodies in their mortuaries and treated 83 wounded. The Palestinian Health Ministry counted 17 dead and 140 wounded, with the higher toll possibly a result of double registration during the initial chaos.
The bloodshed appeared to put Hamas on the defensive for the first time since the Israeli pullout, and gave Palestinian President Mahmoud Abbas greater leverage to enforce a weapons ban.
Under an informal agreement between the Palestinian Authority and armed groups, a ban on displaying weapons was to take effect later on Saturday.
Hasan Yusuf, a Hamas leader, said the group would abide by the ban.
"There will be no military parades in the streets and Hamas weapons will go into the shadows," he said.
Jordan's King Abdullah (R) is to
meet Israeli leader Ariel Sharon
Meanwhile, Jordan's King Abdullah II is to visit the Palestinian territories and Israel "in the next few days" to meet Abbas and Sharon, the official Petra agency reported on Saturday.
"This visit comes in the framework of efforts made by the king to pursue the peace process between Palestinians and Israelis," the agency quoted a palace source as saying.
The meeting will focus on "the need to establish trust between the two (Israeli and Palestinian) parties and to put an end to the violence" as well as "to strengthen the Palestinian Authority and help it extend its power over the territories evacuated by Israel", the source said.
Preparations are under way for a tripartite summit among Abdullah, Abbas and Sharon, a source in the Jordanian capital, Amman, told Aljazeera.